Multiband receiver



Aug. 1, 1939. N, P, CASE 2,168,193

IULTIBAND RECEIVER Filed May 4, 1937 2 Sheets-Sheet 1 AUDlO- FREQUENCY AMPLIFIER FIER INTERIIEDIATE- FREGENCY AMPLI FIG.|.

- INVENTOR. NELSON P. CASE BY J Y ATTORNEY.

' Aug. 1, 1939. N,P ASE 2,168,193

kummmn RECEIVER FIG.2.

m M INVENTOR. 3- NELSON P. CASE ATTORNEY.

Patented Aug. 1, 1939 UNITED STATES PATENT OFFICE MULTIBAND RECEIVER.

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Application May ,4, 1937, Serial No. 140,619

8 Claims.

This invention relates to multiband modulatedcarrier signal receivers and, more particularly, to such receivers operative over a wide range of radio frequencies and including provisions for procuring an approximately uniform amplification at all frequencies of the range.

It has been found diflicult to impart such a characteristic to receivers of the type mentioned. For example, the number of amplifying stages which is adequate to procure the desired gain in a band having relatively low mean frequency is frequently insufficient to procure the desired gain in a band having a relatively high mean frequency, because of the lower attainable gain per stage when operating in the latter band. This difficulty is increased as the difference in the mean frequencies of the bands is increased.

If an automatic amplification control bias is applied to a multielectrode tube used as an oscillator-modulator or frequency changer in such a receiver, such control generally affects to a certain degree the frequency generated by the oscillator, with the result that there is a variation in the oscillation frequency as the amplification control bias varies in response to changes in the amplitude of the received signals. While this variation is only a small percentage of the mean oscillation frequency and, therefore, is not very objectionable when the receiver is operating in a relatively low-frequency band, it becomes particularly objectionable when the receiver is operating in a high-frequency band. Furthermore, if the effect of an increased number of amplifying stages subject to automatic amplification control is provided to procure the desired gain in the high-frequency band, as by reflex amplification of an intermediate-frequency signal, the effective range of automatic amplification control for the high-frequency band is considerably greater than for a low-frequency band.

It is an object of the invention to provide a multiband modulated-carrier receiver which has a minimum number of amplifying tubes and which provides a gain in a high-frequency band or bands approximately equal to that procured in the low-frequency band or bands.

It is a further object of the invention to provide a multiband modulated-carrier receiver of the superheterodyne type in which, in a highfrequency band or bands, frequency variation of the local oscillations with variation in automatic amplification control bias is substantially eliminated and in which the range of the automatic amplification control is approximately the same for all bands of the receiver.

In accordance with one embodiment of this invention, a multiband modulated-carrier receiver comprises a carrier-frequency channel followed by a channel operating at a lower carrier frequency, for example, the intermediate frequency of a superheterodyne receiver. There is also provided means for effectively increasing the number of stages, when the receiver is operating in a bandhaving a relatively high mean frequency, either by reflexing the output of one of the stages of lower carrier frequency through one or more of the stages of higher carrier frequency or by providing for a dual amplification in one of the stages of lower carrier frequency. Also, in accordance with this invention, there is provided 15 means whereby the frequency variation of the local oscillations of a superheterodyne receiver of the type described is reduced or prevented when the receiver is operating in a high-frequency band and whereby the range of the amplification control of the receiver is the same for the low-frequency bandor bands as for a highfrequency band or bands. I For a better understanding of the invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims. Figs. 1 and 2 of the drawings are circuit diagrams, partly schematic, each illustrating an embodiment of the invention as incorporated in a multiband modulated-carrier signal receiver of the superheterodyne type.

Referring now to Fig. l of the drawings, there is shown a circuit diagram of a complete modulated-carrier signal receiver of the superheterodyne type embodying the invention, in which certain conventional portions are indicated schematically since, per se, they form no part of the invention. This receiver comprises, in cascade, an antenna circuit '9, a tunable radio-frequency selector 16, a radio-frequency amplifier tube I0, a tunable radio frequency selector H, a frequency 'changeror oscillator-modulator tube ll provided with an oscillationnetwork 23, an intermediatefrequency selector 51, an intermediate-frequency amplifier l2 of one or more stages, a detector and A. V. C. supply l3, an audio-frequency amplifier I4 of one or more stages, and a loudspeaker I 5.

In order to tune radio-frequency selector networks IB and I! and the oscillation circuit 23, there are provided tuning condensers 28, 29, and 30, respectively, preferably ganged for unicontrol, as shown in the drawings. The radio-frequency 55 selector I6 comprises a group of primary windings 3|, 32, and 33, inductively coupled to a group of secondary windings 34, 35, and 36, respectively, together with switches l9 and 20 for selectively connecting the windings in circuit for operation over the several bands to which the receiver is tunable. Similarly, radio-frequency selector l1 comprises a group of primary windings 38, 39, and 49 inductively coupled to a group of secondary windings 4|, 42, and 43, respectively, and selector switches 21 and 22, while the oscillation circuit 23 includes the inductance windings 45, 46, and 41 to which are coupled the feed-back windings 48, 49, and 50, respectively, and the selector switches 24 and 25. Suitable parallel and series-aligning condensers may be provided for the several tunable circuits, as shown, in accordance with conventional practice. The series-aligning condensers of the oscillation network 23 may be common to the oscillator-grid and oscillatoranode circuits of the oscillator-modulator II, as shown, to provide substantially uniform oscillation voltage, in a conventional manner. Suitable operating potentials are supplied to the input electrodes of tubes I0 and II from sources indicated at +3 and +Sc. Automatic amplification control bias derived from the unit I3 is supplied to the tube I9, to the tube I I (in the two lower frequency bands), and to one or more of the tubes in the intermediate-frequency amplifier 12, all in a conventional manner.

The output circuit of the oscillator-modulator H is coupled to the intermediate-frequency amplifier l2 through a coupling network 51 comprising a pair of double-tuned intermediate-frequency transformers with windings 54, 58 and 60, 6| couplied by a link circuit including windings 59 and 62, inductively couplied to windings 58 and 60, respectively. The transformers 54, 58 and 60, El and their associated windings 59 and 62 are appropriately individually shielded, as indicated.

Neglecting for the moment the operation of the parts of the system involving the'present invention, the system described above includes the features of a conventional superheterodyne multiband receiver. The operation of such a receiver being well understood in the art, detailed explanation thereof is deemed unnecessary. Briefly, however, when operating in the low-frequency or middle-frequency band, a desired modulated-carrier signal intercepted by the antenna 9 is selectively amplified in the radio-frequency selectors I6 and I1 and amplifier l0 and converted in frequency changer H to an intermediate-frequency modulated-carrier signal. This signal is selectively amplified by the intermediate-frequency selector 57 and amplifier l2 and translated therefrom to the detector and A. V. C. supply [3, where the audio frequencies of modulation and the automatic amplification control bias are derived. The audio frequencies of modulation areamplified in the audio-frequency amplifier l4 and reproduced by the loud-speaker IS in a conventional manner. p

Coming now to the parts of the system involved in the present invention, a refiex amplification of the output of frequency changer ll through amplifier tube In is provided in the high-frequency band. To accomplish this, a portion of the intermediate-frequency voltage across winding 58 is applied to the input terminals of amplifier in through conductor 61 and through the radiofrequency choke coil .68, as shown in the drawings.

. A blocking condenser 31, connected in circuit by switch 2 I, prevents flow of intermediate-frequency currents to ground through the relatively lowimpedance path including coil 36, while the choke 68 prevents the by-passing to ground of received high-frequency currents through the lower portion of winding 58.

In considering the operation of the system described above, it will be assumed that, when the unicontrol switches I9, 20, 2!, 22, 24, 25, 26, and 21 are in their lowest or middle positions, as shown in the drawings, the receiver is tuned to a lowfrequency band or a middle-frequency band, respectively. Under these conditions the intermediate-frequency output of oscillator-modulator II is coupled to the input terminals of intermediatefrequency amplifier l2 through the transformer 54, 58, the link circuit including windings 59 and 62,, and transformer 60, 6|, and the operation of the system is conventional, as described above. In the high-frequency band, corresponding to the setting of the switches as shown in the drawings, the link circuit is opened at switch 26, removing the coupling between transformers 54, 58 and 6|], 6 l Under these conditions a portion of the inter-v mediate-frequency output of oscillator-modulator H is coupled through transformer 54, 58 to the input terminals of radio-frequency amplifier l9, wherein it is subjected to a reflex amplification. The output circuit of amplifier II] in the highfrequency band also includes the primary winding 60 of the intermediate-frequency transformer 69, 6|, so that the refiexed intermediate-frequency output of amplifier I0 is applied through transformer 60, 6| to the input terminals of intermediate-frequency amplifier I2, from which it is translated through the rest of the receiver in the normal manner.

While the amplification control bias is applied to both of tubes l0 and II when operating in the lowand middle-frequency bands, it is not applied to oscillator-modulator II in the high-frequency band, thus avoiding the frequency variation of the local oscillations with varying amplification control bias which, as noted above, is particularly seriousin the high-frequency bands. At the same time, a full equivalent range of control is procured in the high-frequency band, since the amplification of the signal is effectively subject to a double control in amplifier l0 through which the signal passes twice.

In Fig. 2 of the drawings there is shown another embodiment of the invention applied, as in Fig. 1, to a receiver of the superheterodyne type. Similar elements in the two figures are identified by the same reference numerals. The receiver of Fig. 2 comprises, in cascade, the antenna circuit 9, tunable radio-frequency selectors l6 and 10, a frequency changer or oscillatormodulator H, provided with an oscillation network 23, an intermediate-frequency transformer H, an intermediate-frequency amplifier tube 12, an intermediate-frequency transformer 13, a detector and A. V. C. supply 13, an audio-frequency amplifier I4 of one or more stages, and a loudspeaker 15. For operation over the several bands of the receiverof Fig. 2, switches I9, 20, 24, 25, 75, and 16 are provided, preferably ganged for unicontrol. Selector l6 is coupled to the input circuit of oscillator-modulator ll through switch 15, selector circuit 10 comprising windings I1 and 18 for the lowand middle-frequency bands, respectively, and switch 16. Automatic amplification control bias derived from unit [3 is supplied to the tube l I, only in the two lower frequency bands and to the tube 12 in allbands of receiver operation. The intermediate-frequency output of amplifier 12 is coupled to the detector and A. V. C. supply unit 13 through transformer 13, comprising windings 19, BU'With their associated tuning condensers, in all bands of receiver operation.

Againheglecting for the present the operation of the parts of the system involving the present invention, the system described above includes the features of a conventional superheterodyne multiband receiver. When operating in either of the two lower frequency bands, a desired modulated-carrier signal intercepted by antenna 9 is selectively amplified in selectors l6 and 10 and converted in frequency changer I l to an intermediate-frequency modulated-carrier signal. The intermediate-frequency signal is selectively amplified by the transformer N, amplifier 12, and transformer 73 and translated therefrom to detector and A. V. C. supply [3, where the audio frequencies of modulation and the automatic amplification control bias voltage are derived. Beyond this point, the operation is identical with that described in connection with Fig. 1.

Coming now to the parts of the system in-Fig. 2 involved in the present invention, a dual amplification is effected in amplifier tube 12 in the high-frequency band. In accomplishing this, the carrier-frequency signals selected by selector IS in the high-frequency band are applied to the grid of tube 12 through the condenser 31. A loss of these signals to ground through the tuned circuit comprising the secondary of intermediatefrequency transformer 1| is prevented by the radio-frequency choke coil 68. The amplified carrier-frequency output of amplifier tube 12 is then applied to the input terminals of frequency changer H through the radio-frequency transformer 83, 82, the secondary winding 82 being tuned by tuning condenser 29. The intermediate-frequency output of the frequency changer l l is selectively translated through the intermediate-frequency transformer II and applied to the input terminals of amplifier 12 through the radiofrequency choke 68. The condenser 31 is of relatively low capacitance and serves to prevent the intermediate-frequency currents from draining off to ground through the relatively low-impedance path including winding 36.

As in the system described in Fig. 1, the A. V. C. bias is not applied to the oscillator-modulator II in the high-frequency band. Full equivalent automatic amplification control is procured in the high-frequency band of Fig. 2, since the signal is effectively subjected to a double amplification in the controlled amplifier tube 12, through which the signal passes twice.

While there have been described what are at present considered to be the preferred embodiments of the invention, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the spirit and scope of the invention.

What is claimed is:

1. A multiband modulated-carrier signal receiver having a plurality of stages and tunable over a high-frequency band and one or more low-frequency bands comprising, a first modulated-carrier-frequency channel, a frequency changer coupled to said channel for changing the carrier derived from said channel to a carrier having a different frequency, said frequency being of a different order of magnitude than that of said first channel in said high-frequency band, a second carrier-frequency channel tuned to the frequency of said second carrier coupled to said frequency changer, an amplifier in one of said channels, an automatic amplification control means connected to a plurality of said receiver stages including said frequency changer and said amplifier, and means for selectively including said amplifier in both of said channels and for simultaneously reducing the effect of said automatic amplification control on said frequency changer for operation in said high-frequency band.

2. A multiband modulated-carrier signal receiver tunable over a high-frequency band and one or more low-frequency bands comprising, a multiband carrier-frequency selector system, an amplifier in said system, a frequency changer coupled to said amplifier, a signal-trantlating stage, first and second intermediate-frequency transformers, a link circuit coupling said transformers, and means for selectivelycoupling the output of said frequency changer to said translating stage, either through said firsttransformer, saidlink circuit and said second transformer and for simultaneously conditioning said selector system for operation in said low-frequency band or bands, or through said first transformer, said amplifier and said second transformer and for simultaneously conditioning said selector system for operation in said high-frequency band.

3. A multiband superheterodyne signal receiver tunable over a high-frequency band and one or more low-frequency bands comprising, a multiband carrier-frequency selector system, an amplifier in said system, a frequency changer coupled to said amplifier, a signal-translating stage, first and second carrier-frequency. selectors, means coupling said selectors, a plurality of switch means for selectively conditioning said receiver for operation in any of said bands, switch means for selectively coupling the output of said frequency changer to said translating stage, either through said first selector, said coupling means and said second selector for operation in said low-frequency band or bands, or through said first selector, said amplifier and said second selector for reflex amplification of the intermediate frequency in said high-frequency band, and unicontrol means for operating said switch means.

4. A multiband modulated-carrier signal receiver comprising a plurality of stages and tunable over a high-frequency band and one or more lowfrequency bands comprising, a multiband carrierfrequency selector system, an amplifier in said system, a frequency changer coupled to said amplifier, a signal-translating stage, automatic amplification control means coupled to a plurality of said stages, means for selectively coupling the output of said frequency changer to said signaltranslating stage, either directly and for simultaneously conditioning said selector system for operation in said low-frequency band or bands, or through said amplifier and for simultaneously conditioning said selector system for operation in said high-frequency band, and means effective in said high-frequency band to reduce the effect of said automatic amplification control means on one of the receiver stages without substantially reducing the range of amplification control.

5. A multiband modulated-carrier signal receiver comprising a plurality of stages and tunable over a high-frequency band and one or more low-frequency bands comprising, a multiband carrier-frequency selector system, an amplifier in said system, a frequency changer coupled to said amplifier, a signal-translating stage, automatic amplification control means coupled to a plurality of said stages,a plurality of switch means for selectively conditioning said receiver for operation in any of said bands, switch means for selectively coupling the output of said frequency changer to said translating stage, either directly for operation in said low-frequency band or bands, or through said amplifier for reflex am-- plification in said high-frequency band, switch means to reduce the effect of said automatic amplification control means on one of the receiver stages without substantially reducing the range of amplification control, and unicontrol means for operating all of said switch means.

,6. A multiband modulated-carrier signal receiver having a plurality of stages and tunable over a high-frequency band and one or more lowfrequency bands comprising, a multiband carrier-frequency selector system, an amplifier in said system, a frequency changer coupled to said amplifierfa signal-translating stage, automatic amplification control means coupled to a plurality of the receiver stages including said frequency changer, means for selectively coupling the output of said frequency changer to said signal-translating stage, either directly and for sifrequency selector system,an amplifier in said system, a frequencychanger coupled to said amplifier, a signal-translating stage, a plurality of switch means for selectively conditioning said re-., ceiver for operation in any of said bands, automatic amplification control means coupled to a plurality of the receiver stages including said fre quency changer, switch means for selectively coupling the output of said frequency changer to said signal-translating stage, either directly and for simultaneously conditioning said selector system for operation in said low-frequency band or bands, or through, said amplifier and for simultaneously conditioning said selector system for operation in said high-frequency band, switch means effective in said high-frequency band to reduce the effect of said automatic amplification control on said frequency changer and increase the effect thereof on one of the other receiver stages, thereby to procure substantially the same range of automatic amplification control in all bands, and unicontrol means for operating all of said switch means.

8. A multiband modulated-carrier signal receiver having a plurality of stages and tunable over a high-frequency band and one or more lowfrequency bands comprising, a multiband carrier-frequency selector system, a frequency changer comprising output terminals, a signaltranslating channel coupled to said output terminals, an amplifier in said signal-translating channel, automatic amplification control means coupled to a plurality of the receiver stages including said frequency changer and said amplifier, means for selectivelyincluding said amplifier in both of said channels and for simultaneously conditioning said selector system for operation in said high-frequency band, and means effective to reduce the effect of said amplification control on said frequency changer when operating in said high-frequency band.

NELSON P. CASE.

Cit 

